In many metal working chip forming operations it is desirable to deliver a coolant directly to the working edge. The purpose of the coolant is not only to cool the working edge but also to assist in chip removal. The most straightforward and easiest to manufacture coolant channels are axially directed. This can be done by simply drilling a central bore, or two parallel axially directed bores in the tool. In drills, twisted or helical channels are also used. In drills with replaceable cutting inserts spaced at different radial distances from the axis of rotation it is desirable to direct the exit opening towards the cutting inserts. U.S. Pat. No. 5,676,499 there is described a process wherein straight holes are drilled at different radial distances in a cylindrical blank. The middle portion of the blank is then heated and twisted giving rise to spirally formed channels. At the end of the process exit channels are drilled at an angle to the centerline of the drill resulting in exit openings that are spaced at different radial distances from the centerline, in the vicinity of the cutting inserts.
Another method for obtaining complex shaped coolant channels is to use a core such as copper or wax in a powder body and then sinter. The core can be of any desired shape. During the sintering operation, the core disappears into the pores of the powdered body by infiltration leaving a cavity of configuration corresponding to the shape of the core.